The production of high octane gasoline continues to be a major objective of refinery operations worldwide. The phase-out of lead and the movement to reformulate gasoline to improve air quality in the United States, Europe, and the Pacific Rim countries present a major challenge in the refining industry. In the United States, the recent Clean Act Amendments define reformulated gasoline in terms of properties such as RVP (Reid Vapor Pressure) and composition including oxygen, benzene, and total aromatics contents, as well as in terms of performance, measured by reductions in volatile Organic Compounds (VOC) and gaseous toxic effluents. More stringent requirements may be required in the future as indicated by California Air Resources Board proposals for further limitations on gasoline olefins, sulfur, RVP, and distillation parameters.
In most of the regulatory schemes now under consideration, limitations will be placed on the permissible level of benzene in motor gasolines. Much of the benzene in motor gasoline comes from reformate which is a major high octane contributor and therefore desirable from this point of view. Given the need for high octane fuel in current engine designs, the requirement for reforming as a source of octane will continue but only if the benzene levels can be held at permissible levels.
Pat. No. 4,827,069 (Kushnerick) describes a process for alkylating the aromatic components in reformate with light olefins from FCC off gases, to produce high octane alkyl aromatics which are less toxic than benzene. The process is carried out by passing the reformate and the light olefin co-feed into a fluidized bed of catalyst, preferably ZSM-5, at a temperature which is typically in the range of 500.degree. to 800.degree. F. The ethylene and propylene components of the light olefin feed react to produce olefins, paraffins and aromatics which have a higher product value than the feed components. In addition, the feed components react with the aromatics in the reformate to produce alkyl aromatics which themselves may rearrange and transalkylate over the catalyst to produce a further range of products. U.S. Pat. No. 4,992,607 (Harandi) also describes a process for upgrading reformate using FCC fuel gas as a source of olefins for alkylation of the aromatic components present in the reformate.
U.S. Pat. No. 4,950,387 (Harandi) describes a process in which a naphtha stream is upgraded by reaction with light olefins such as FCC fuel gas. The naphtha may be a light FCC naphtha, a heavy FCC naphtha or a heart cut of heavy naphtha drawn from the FCC column.
In all cases where a reformate is treated in these processes, the benzene content is reduced during the process by the alkylation reactions over the catalyst. It would, however, be desirable to reduce the benzene levels still further.